The uniform flow of fluids through packed beds of particulate material is important for the efficient operation of pressure or temperature swing adsorption systems and fixed-bed chemical reaction systems. Any significant radial variation of the fluid axial velocity will reduce effective fluid-solid contacting, thereby reducing the product purity and recovery in adsorption systems and reducing the overall conversion in a chemical reactor. The uniform flow of fluids through a packed bed of particulate material can be realized by careful loading of the particulate material into a vessel to form a dense, uniform bed with a consistent and minimum bed porosity.
Different types of particle loading methods have been utilized in the art to form particulate beds in vessels. The first and oldest of these methods is dump loading, in which the particulate material is simply poured into the vessel and manually leveled. There is no control over the bed uniformity in this method and the particles are not well settled, even though vibration can be used during or after dumping to settle the bed. Because a dense, uniform bed is not formed, this method does not guarantee a uniform radial distribution of fluid flowing through the bed.
A second method has been used in which a particulate bed is built by depositing a succession of bulk layers of particles in a vessel. One well-known version is the sock loading method, which uses a chute or flexible tube to transport particles from a hopper above the vessel to the surface of the bed. As the vessel is filled, the chute is raised until the bed installation is complete. This method does not yield a dense, uniform bed because the particles are randomly oriented and are subject to uneven settling.
A third method, radial dispersion, has been used in which the particles are thrown radially outward from a rotating dispersing device and then fall essentially as individual particles to the bed surface. In this method, a stream of particles is dropped onto a rotating apparatus, such as a plate or series of horizontal rods, and the rotating apparatus breaks up the particle stream and imparts radial motion to the individual particles as they fall to the surface of the bed. By making the particles fall individually, the radial dispersion method allows for dense loading, but the particle dispersion over the bed surface is random, so the final bed surface may not be uniform.
A fourth method of particle loading is described as dispersed dropping. In this method, the particles are passed through one or more holes and dispersed over the bed surface. The holes may be either stationary or moving relative to the bed. In one version, a series of fixed plates with increasing numbers of holes breaks the particle flow into smaller and smaller streams. While the final particle substreams may be uniform, the particles do not fall individually unless the drop height is large. As the surface of the bed rises, the drop height decreases, and the packing density decreases as a result. More recent versions of the dispersed dropping method utilize hollow rotary arms with spaced holes through which particles flow and drop to the bed surface as the arms rotate above the bed. This method results in dense, uniform beds and is a generally preferred method for particle loading.
In the dispersed dropping method of particle loading used in the art, particles typically are distributed by flow through a large number of small orifices to achieve the desired degree of dispersal. Dispersal through a smaller number of larger orifices would be desirable if proper loading dispersion could be achieved. The present invention, which is disclosed below and defined by the claims which follow, offers an improved method of dispersed dropping by means of rotary arms which utilize a combination of relatively large orifices and adjacent particle dispersal assemblies to effect uniform dispersal of particles to form a dense, uniform bed in a vessel.